程序问题，求助

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class _5_08 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        Image1.Visible = false;
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        string strDir = FileUpload1.PostedFile.FileName;
        int myPos = strDir.LastIndexOf("\\");
        string strName = strDir.Substring(myPos);
        string strType = strName.Substring(strName.LastIndexOf(".") + 1);
        string strPath = Server.MapPath(".") + strName;
        if (strType == "jpg" || strType == "gif" || strType = "bmp" || strType = " png")
        {
            FileUpload1.SaveAs(strPath);
            Image1.ImageUrl = strName;
            Image1.Visible = true;
            Response.Write("图片上传成功");
        }
    }
}


 运算符“||”无法应用于“bool”和“string”类型的操作数，怎么解决？

 LastIndexOf("\\")和Substring（）是什么意思？
希望大家帮我一下，谢谢各位了。




上面的问题解决了又出现这样的问题：在这句string strName = strDir.Substring (myPos);出现
System.ArgumentOutOfRangeException: StartIndex 不能小于 0。 怎么办？

[[it] 本帖最后由 zore0 于 2008-9-22 13:27 编辑 [/it]]